Imaging systems such as infrared cameras typically employ baffles to block stray light rays from reaching system detection elements at the image plane of the system. These detection elements typically include one or two-dimensional arrays of detectors arranged in the image plane. Infrared detectors typically respond to low-energy photons which are emitted by all warm surfaces at or around room temperature (200.degree. K-300.degree. K), including the baffle and other system components. These self-emissions can strike the detection elements and "fog" the scene being imaged. The effect especially impairs performance of systems like infrared cameras since their detectors are designed to react to low-energy photons and are therefore extremely sensitive. To reduce self-emission, the components of imaging systems are typically cooled to a temperature between about 16.degree. K and 195.degree. K by a mechanical cryogenic refrigeration subsystem connected to or within the camera. Alternatively, the components can be cooled by coupling them to a reservoir containing liquid air, liquid nitrogen or liquid helium. To prevent frosting of the system components and to minimize the cooling burden on the refrigerator, the cooled components are mounted in a vacuum chamber such as a Dewar case fitted with an entrance window to allow light to reach the detection element.
Depending upon its size, the mechanical refrigeration subsystem can consume large amounts of power and can cause vibration which impairs the optical performance of the system. The larger the refrigerator, the greater the power consumption and vibration. The principal factor driving the size of the refrigerator is the size of the cooling load it is required to handle. If the system cooling load is reduced, a smaller refrigerator is required, resulting in reduced system power consumption, weight, cost and vibration and improved system performance. Where a cooling reservoir is used, a reduced cooling load would reduce the amount of the cryogen consumed in cooling the system. It has been estimated that prior conventional cold shielding devices which include cylindrical stray light baffles constitute at least half the cooling burden of an infrared camera.